Understand Peak Flow Charts

The Peak Expiratory Flow (PEF) is a measurement of how much air flows through the airways in the lungs. If the airways are narrowed, as in episodes of asthma, then the readings are lower.  By recording and charting these readings we can better understand your asthma.

There are four main patterns of peak flow charts that are suggestive of asthma.  But first we will examine the chart of a healthy person.

Good Chart

The above chart shows readings with small variation in readings. This chart has a percentage change in PEF of less than 20%. This type of chart is seen in people who have well controlled asthma or those who do not have asthma.

The important results that will help doctors and asthma nurses to diagnose asthma from the peak flow charts are:

  • A variation between readings of more than 20%
  • An increased difference between the morning and evening readings
  • An early morning dip in the readings

Large variations

The above chart shows a large variation in peak flow reading from day to day. A chart like this would help to confirm the diagnosis of asthma. For someone with asthma a chart like this would indicate poor control and more treatment is required.

Morning Dips

A peak flow chart showing early morning dips in the readings would help to confirm the diagnosis of asthma. For someone with asthma, this chart indicates poor control and more treatment is required.



This chart shows readings that are dropping from day to day. This person has poorly controlled, deteriorating asthma. Urgent help is required.


This peak flow chart shows a gradual improvement in readings. This is normally seen after someone has started asthma treatment.

This Web site is not a substitute for professional medical advice. Materials available through this Web site are for informational purposes only. You should contact your physician if you have any questions about your medical condition, or if you need medical help. If you need emergency medical help, you should immediately call 999 or your physician.